Toe Overlap on Charge Mixer

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531colin
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Re: Toe Overlap on Charge Mixer

Postby 531colin » 7 Jul 2011, 12:43am

thirdcrank wrote:
531colin wrote:... The usual measure is "front centres" ...
Which immediately draws attention (or mine, at least) to crank length. Since every mm makes a difference, edging up to 175mm cranks as the norm can't help.


Something else I don't understand....my designs allow for short cranks on the small bikes, long cranks on the big bikes....all you have to consider is front centres for toe clearance, and BB height for cornering and for getting a foot down when stopping. Its not hard, is it?

snibgo
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Re: Toe Overlap on Charge Mixer

Postby snibgo » 7 Jul 2011, 1:43am

Thanks for the correction. I was confusing the two models.

Taking your dimensions: the Spa Audax has 620 - 340 - 175 = 105mm for my toes, where I need at least 110mm. It's somewhat tight, and leaves no room for mudguards.

But the Spa Tourer has 656 - 388 - 175 = 133mm for my toes, which is enough, and has room for mudguards.

I note my Raleigh tourer has dimension "H" (rear axle to BB) 440mm. The Spa Audax has 425mm, and the Spa Tourer is a more generous (up to) 460mm, allowing for more heel clearance from panniers.

(Pannier heel clearance should be fixed by pannier manufacturers, but most current models have the front face too vertical.)

Good stuff.

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531colin
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Re: Toe Overlap on Charge Mixer

Postby 531colin » 7 Jul 2011, 7:32am

Snibgo
In the clearer light of morning, I have worked out where we are going wrong. I knew it didn't make sense last night, now I know why!

Toe overlap, of course, happens when you turn the bars. Turning the bars has the effect of moving the mudguard forward, giving an important bit of extra clearance, by the time the 'guard is turned far enough to be level with your toes...it moves in an arc, of course, when viewed from the saddle. :roll: (hey ho! "past my bedtime" . I really have to stop trying to do stuff after about 9.30! :roll: )

The toes of my shoes are 100mm from the centre of my cleats, I get toe clearance on all the bikes, even the smallest.
You might not get clearance on the smallest audax bike, but I guess if you are riding 175mm cranks you won't be riding the smallest bike!

CJ tested (and bought) the 54cm tourer (front centres 625mm)...I know he would have told us if he got overlap!

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Re: Toe Overlap on Charge Mixer

Postby thirdcrank » 7 Jul 2011, 7:46am

531colin wrote: ....CJ tested ...
and that's probably the crucial bit: I take it to mean tried for size and that's much more likely to achieve satisfaction than referring to a spec sheet.

There's an invitation somewhere further up to bring your own pedals. Bearing in mind the number of bikes sold without pedals, that's probably very important for anybody wanting to test a new bike before buying.

In short,one more reason for buying personally from a shop.

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531colin
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Re: Toe Overlap on Charge Mixer

Postby 531colin » 7 Jul 2011, 8:04am

thirdcrank wrote:.............

There's an invitation somewhere further up to bring your own pedals. Bearing in mind the number of bikes sold without pedals, that's probably very important for anybody wanting to test a new bike before buying..............


There are just so many pedal systems now, I think the best way to get a proper test ride is to bring your shoes, and some pedals you are used to.
We might not have your favourite pedals knocking around, and you need to concentrate on the bike you are testing, not be worrying about getting your foot out when riding an unfamiliar bike on unfamiliar roads.

CJ's test here http://www.ctc.org.uk/resources/Magazine/201107062.pdf

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Re: Toe Overlap on Charge Mixer

Postby MartinC » 7 Jul 2011, 1:37pm

Toe overlap is a function of the frame design and many other things too so designing a frame that doesn't allow toe overlap is a tall order. Sure you can design a frame that doesn't have overlap for normal (i.e. exactly like me) people. If you design a frame that won't have overlap for a clown (in clown shoes) who rides with his heels on the pedals then we'll all be riding recumbent trikes.

Toe overlap in any given frame will depend on:
- fork rake
- rim size
- tyre size
- if and how mudguards are fitted
- crank length
- Q factor
- foot size
- shoe size and type
- cleat position (laterally and fore/aft) if used
- toe clip size if used
- where the user decides to put their foot if flat pedals are used.

Toe overlap doesn't bother me but I can very well understand the concerns that others have even if I don't think there's a real problem. If you're a knowledgeable cyclist then you need to work out and remember what front centre distance you need on a bike. If you want to make a big fuss about it at point of sale then you'll probably just reinforce the prejudice that cycling's dangerous and should be banned. It's an amusing contradiction that we want safety regulations for a vehicle that can't even stay upright by itself! If we were logical we'd make full chaincases and stabilsers compulsory and ban foot retention devices.

I just don't think it's worth having a standard for this - it'll either be meaningless of we'll stop a lot of people having perfectly sensible frames.

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Re: Toe Overlap on Charge Mixer

Postby thirdcrank » 7 Jul 2011, 2:39pm

531colin

Your reply makes it sound as though I came across as having a go at you which was certainly not my intention. Quite the contrary. I was trying to agree that testing before buying was a good idea. I've never bought a bike from Spa Cycles but plenty of posters refer to a generous test ride policy there.

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CJ
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Re: Toe Overlap on Charge Mixer

Postby CJ » 7 Jul 2011, 2:48pm

snibgo wrote:Yes, thanks, Colin.

My wheel radius (with 28mm tyres, ignoring mudguard) is 350mm, and my crank is 175mm, total 525mm. The maximum Spa dimension I is 620mm, leaving 95mm from pedal axle to tyre.

So I would have toe overlap on the Spa tourer, even without mudguards.


The calculation of toe clearance if far from such a simple calculation as that. The wheel swings in an arc as you steer, so you have a lot more clearance than there would appear to be when the bike is viewed from the side with the wheel pointing straight ahead.

The mathematics to describe the actual path swept out by the tyre is almost beyond my trigonometrical skills, but as a first approximation one may assume the wheel pivots about the front hub centre and use simple pythagoras on the triangle formed by the wheel tyre outer radius (hypotenuse) and distance from the centreline of the bike to the centre of the left pedal (closer inboard whenever there is any difference).

Subtract the resulting "effective radius" dimension from the front centres. Also subtract whatever mudguard clearance you need (my rule of thumb is half the tyre section) and of course the crank length.

What you have left is toe clearance - sort of. You also need to subtract about 5mm to allow for the convex curved shape of the toe of a shoe (the side of the toe hits a wheel that clears the tip of the toe by about that much).

So: assuming your pedal is about 130mm off-centre to the bike, the effective radius of that 350mm radius wheel is approx 325mm. Subtracting that, a 175mm crank and the 5mm curvature allowance from 620mm leaves 115m of toe clearance.

That's a lot better, but still leaves nothing much for a mudguard. However, as 531Colin has pointed out, some of your other numbers are unduly pessimistic. A normal 28mm tyre radius is 10mm less than your 350mm. Not everybody uses 175mm cranks. And yer average audax type is so highly influenced by old racing myths about wheelbase and new superstitions around steering geometry that I can forgive Spa for not daring to make them any longer.

The largest size touring bike's front centres of 656mm, with 32mm tyres, 16mm of guard and 175mm cranks, has by my estimation a toe clearance of 143mm. I've not also checked out my shoe size data but I think that probably allows for yer actual pedalling bigfoot! :)
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rootes
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Re: Toe Overlap on Charge Mixer

Postby rootes » 7 Jul 2011, 3:20pm

i'm not sure what all the fuss about toe overlap is about.. never found it an issue on bikes where you have overlap - just need to learn to the ride in a certain way

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531colin
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Re: Toe Overlap on Charge Mixer

Postby 531colin » 7 Jul 2011, 3:33pm

thirdcrank wrote:531colin

Your reply makes it sound as though I came across as having a go at you which was certainly not my intention. Quite the contrary. I was trying to agree that testing before buying was a good idea. I've never bought a bike from Spa Cycles but plenty of posters refer to a generous test ride policy there.


T.C.......It never ocurred to me that you were "having a go", sorry if I gave that impression.
And yes, we do like customers to ride our test bikes, for as long as is needed.

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Re: Toe Overlap on Charge Mixer

Postby snibgo » 7 Jul 2011, 4:12pm

531colin wrote:Toe overlap, of course, happens when you turn the bars.

Ah, yes, so it does. My brain wasn't engaged. I'll have to think further.

I was struck by the fact that my bike's "I" dimension is the same as the Spa Audax 58cm model. So assuming the same crank, rim, tyre and steering geometry, the TO would be the same. But the steering geometry could easily be different.

Harrowgate isn't a million miles from Skipton, so I may be able to pop in towards the end of the month, just out of curiosity.

Of course, I also support trying a bike before buying. Like a pair of shoes, the right fit is important.

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531colin
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Re: Toe Overlap on Charge Mixer

Postby 531colin » 7 Jul 2011, 4:30pm

In the meantime, I'll see if I can get some photos like Dan Joyce's shot in his review of the Audax.

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Re: Toe Overlap on Charge Mixer

Postby Freddie » 7 Jul 2011, 5:08pm

Toe overlap is dangerous on all but racing cycles, any bike used normally should not have it, period (as the Americans like to say).

Of course you can learn to ride with it, but you can also learn to ride with too short chainstays where your feet clip the panniers and the front wheel unweights in a seated ascent, not to mention steep angles where the front wheel won't track a straight line and you can't get the saddle back far enough...oh wait, the majority of us do, because the majority of frame design (though design is stretching it, I'd prefer to call it marketing) these days is crap and copied over ad hoc from the next guy. Because if everyone's doing it, it must be right?.

Personally, I wouldn't buy such a compromised bicycle. To the OP who didn't realise 95% of bicycles these days are compromised in such a way, I'd take it back for a refund as not fit for purpose/dangerous.

I'd wish there were less apologists for bad design here than there are, this stuff matters far more than the latest Campagnolo groupset or high tech steel and it's high time manufacturers were taken to task about poor, even dangerous designs.

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Re: Toe Overlap on Charge Mixer

Postby Vorpal » 7 Jul 2011, 5:14pm

Why is toe overlap dangerous on my road bike, but not on a racing bike?
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Re: Toe Overlap on Charge Mixer

Postby CJ » 7 Jul 2011, 5:21pm

MartinC wrote:Toe overlap is a function of the frame design and many other things too so designing a frame that doesn't allow toe overlap is a tall order.

Not really. It's a moderately complex excercise in geometry that should be well within the capability of any competent design engineer. The real problem is that they can't easily get the forks and stems to go with that design due to the limited choice in offsets of both, the dimensions of which slavishly mimic what works for actual racing, where nobody uses mudguards, or goes slowly enough uphill to wobble, or has to negotiate cyclepath obstacles, etc.

Sure you can design a frame that doesn't have overlap for normal (i.e. exactly like me) people.

But quite often the designers fail - or are prevented by standard forks and stems in even that simple task! :shock:

If you design a frame that won't have overlap for a clown (in clown shoes) who rides with his heels on the pedals then we'll all be riding recumbent trikes.

I'll ignore that for now - but only for now. :twisted:

Toe overlap in any given frame will depend on:
1- fork rake
2- rim size
3- tyre size
4- if and how mudguards are fitted
5- crank length
6- Q factor
7- foot size
8- shoe size and type
9- cleat position (laterally and fore/aft) if used
10- toe clip size if used
11- where the user decides to put their foot if flat pedals are used.

I've added numbers to this list to deal with it better.

1, 2, 3 and 4 are a function of the design of the bike and hence entirely within the designer's control. The correct fork offset is dictated by the head angle, fit something more than a few mm different and the bike will not handle as it should. Rim and tyre size is limited by the clearance, and it would be plain weird to fit a fatter tyre in front than the frame could handle just becasue the fork had more clearance. Nobody is suggesting that designers should cater for weird stuff (except you with your clowns :lol: ). Mudguards likewise are a matter of the design clearance and presence of fittings. No eyes, no clearance expected, is what the standards say already and that's fair enough.

6 does not vary enough to worry about and sufficiently predicted by the type of bike that type of frame is for.

5, 7 and 8 are a function of the size of rider a particular size of frame is for. A professional designer uses tables of anthropometric data to ensure that, for example, 90% of the relevant population segment are catered for. In cycling the limited range of available crank lengths makes his job easier in fact. Apart from clowns, the length of shoes does relate pretty well to the size of foot.

For 9 and 11 it is not necessary for a designer to cater for anything far off the known biomechanically optimum positioning.

Regarding 10: a thin steel toeclip adds insignificantly to the forward projection of the shoe alone. Plastic ones add something, but who still uses toeclips? I would not argue with a designer who said it was not necessary to take account of them.

However, if we're talking about the offer for sale of complete made-up bikes, which is what we were talking about regarding those Charge Mixers and it what the European Standards are about - not frames only - then the complete specification of the bike is fixed and known. This fixes most points of variation: 1,2,3,5,6 and 10, and makes 4 closely predictable. All that remains is the 90 percentile foot, hence shoe size and toe projection of the riders this bike is sized for - a simple matter of ergonomics.

It's not a difficult job to do if they want to do it. Given the motivation the designers will in turn demand from component suppliers the necessary close-up stems and forks with extra offset befitting the shallower head angles they'll have to use. They won't look exactly like the bikes the pros ride in the Tour, but near enough that only you or I will spot the difference. And they will actually handle just as well. The factoid of poor handling with shallow head angles arises from putting a standard fork in such a frame. Fractionally longer front centres will improve the stopping distance, and 99.99% of those who buy ready-made bikes will never lean over far enough in a corner, or hold the bars steady enough while they do that, for a minuscule fraction less weight on the front wheel to make any diference at all to whether it washes out.

Toe overlap doesn't bother me but I can very well understand the concerns that others have even if I don't think there's a real problem. If you're a knowledgeable cyclist then you need to work out and remember what front centre distance you need on a bike. If you want to make a big fuss about it at point of sale then you'll probably just reinforce the prejudice that cycling's dangerous and should be banned. It's an amusing contradiction that we want safety regulations for a vehicle that can't even stay upright by itself! If we were logical we'd make full chaincases and stabilsers compulsory and ban foot retention devices.

There's nothing wrong with offering an informed choice and managing customer's expectations. I reject totally, your implication that those of us who do object to toe overlap are lacking in cycling skill. I certainly can ride a bike with overlap, sometimes I have to test ride them, but I don't like it and don't see why this should be foisted onto customers without so much as a by your leave. Yes, bicycles are fundamentally unstable vehicles, which makes it more rather than less important that unnecessary extra ways of falling off them are avoided - except by those who delight in circus tricks of course. :wink:

I just don't think it's worth having a standard for this - it'll either be meaningless or we'll stop a lot of people having perfectly sensible frames.

You're welcome to your opinion but I think you know in your heart of hearts that it isn't actually too difficult for a designer to ensure that 90% of the people buying a given size of complete bicycle, provided it is the right size for them and they ride it correctly, will not experience the problem. And for standards to address this is not difficult. They pretend to do it already and just need some sensible numbers to sort it out. This will probably force the standards writers to adopt a sliding-scale approach rather than one-size fits all, which will be a very good thing generally. (This aspect of the new standards has caused untold problems for manufacturers who've had to beef up perfectly good frame designs, so a small rider is lumbered with an overweight bike strong enough to carry someone twice their size - but that's another story!)

As for "perfectly sensible frames", these standards do not apply to frames alone, only complete bikes. Frames can be designed any which way and you are and forseeably will always be able to buy them, as frames. Frames don't get caught by any standards and Bicycle sales safety regulations unless they are first assembled into a bike and then sold by a retailer as a complete bike. If the frame and fork and other components of the customer's choosing are sold in one transaction, as bicycle parts, and the customer pays the shop separately to assemble them into a bike, there should be no problem.

However I think it would be better if there were provided a more obvious means for someone to buy complete bikes of a configuration that shops is not legally allowed to sell (even it some of them already do), such as one with the brake levers the other way round. Surely all it needs is a simple form for customers to sign to say they are aware of and agree to this, that and the other itemised deviations from the usual standard. No mass manufacturer is going to want those forms hanging around his bikes, so they'll all toe the line :wink: . But it then becomes totally straightforward for the more specialist suppliers to offer something different, to meet unusual customer demands, to innovate and maybe push the design envelope in ways that eventually benefit the mainstream.
Chris Juden
One lady owner, never raced or jumped.